In refrigeration or air conditioning systems, motor operating temperature is typically controlled in one of three ways. First is suction gas cooled which can be employed where the suction gas flow rate is sufficiently high and the temperature is sufficiently low that an appropriate motor operating temperature can be maintained by heat transfer between the hot motor and the cold suction gas. Second is discharge gas cooled where the discharge gas temperature controlled motor is typically controlled by maintaining adequate discharge flow rate and discharge temperature below the maximum safe operating temperature of the motor. Depending upon the condition, liquid injection is commonly utilized to augment discharge temperature control. Third is economizer gas cooled. Economizers are typically controlled by relying on the saturation pressure and superheat for control of the vapor going to the compressor. In some cases, a flash economizer is utilized with vapor theoretically at the saturation temperature. However, the flow rate and temperature differential between the motor to be cooled and the economized vapor is inadequate to keep the motor sufficiently cool for reliable operation. In such cases when economizer vapor is inadequate to keep the motor cool, flooding of the economizer is employed, i.e. liquid refrigerant is allowed to be entrained with the vapor to provide additional cooling. The problem that this presents is that no device is available which can accurately maintain the mixture of liquid and vapor to yield a specific outcome as it relates to the motor temperature that is to be controlled.
Commonly assigned U.S. Pat. No. 5,582,022, filed May 18, 1995 which is a continuation-in-part of U.S. patent application Ser. No. 08/167,467, filed Dec. 14, 1993, and now abandoned, and U.S. Pat. No. 5,475,985 each disclose structure for motor cooling.